Tannin-Based Carbon Foams for Electromagnetic Applications

Broadband dielectric analysis of tannin-based carbon foams produced at nine different densities, ranging from 0.036 to 0.114 g/cm³, was carried out in wide frequency (20 Hz-35 GHz) and temperature (25-500 K) ranges. Both dielectric constant and electrical conductivity of carbon foams in quasi-static regime, at 129 Hz, were high (more than 10⁶ and close to 70 S/m, respectively), and increased with carbon foams density according to power laws. Significant electromagnetic interference shielding efficiency (EMI SE) was found at microwave (MW) frequencies for all produced samples. The highest value of electromagnetic attenuation at the level of 20 dB for 2-mm thick sample was observed for the foam having the highest density and the lowest mean cell size. For thicker samples (4 mm and 1 cm), EMI SE reached 39 and 73 dB, respectively. On cooling, dc conductivity decreased with temperature according to Mott´s law but foams still remained opaque to the MW radiation. MW performances of carbon foams reported here, along with other valuable properties such as “green” origin, low price, lightness, chemical inertness, thermal stability and high conductivity, open new routes for producing effective EMI shields from tannin-based carbonaceous porous structures.